I'll give you a general pointer that you're unlikely to see coaches talk about or even use themselves -- although it would help them become better coaches.
Once, I was on a court and the mother a 5 years old tried to explain to him how to hit and move on a court. She emphasized the importance of the ready position, telling the kid not to set up for a forehand or a backhand until he knew that one or the other would come. What struck me wasn't so much the content than the form. She was literally making an argument, justifying it on the basis that setting up would, provided a wrong side-selection, cause the kid trouble.
If you didn't get where's the problem yet, there's a problem with your coaching. The form of the mother's speech was basically deductive: if A, then B. This sort of hypothetical scenario in which some application yields a conditional results relies unto a propositional logic, which is part of formal operations, not concrete operations and formal operations are not possible before puberty... The kid cannot possibly make sense out of a deductive argument.
How to solve the problem? Easy: put the kid in a concrete situation where the conditions makes your argument possible. That is, instead of mentally hypothesizing a ball to the forehand when he's set up for a backhand (or vice-versa), literally make that situation happen: send him a ball on the wrong side every time he sets up too early.
The take homes? Adapt your speech to your audience and instead of focusing on what you say, focus on what the audience members get out of your speech.
“For most Americans, economic growth is a spectator sport.” -P.R. Krugman